The invention relates generally to electric-actuated automotive emission control valves, and more particularly to exhaust gas recirculation (EGR) valves for internal combustion engines that power automotive vehicles.
A solenoid is a known electric actuator for an EGR valve. The solenoid comprises an electromagnet coil and a stator having an air gap at which magnetic flux acts on an armature. The armature motion is transmitted to a valve member to allow flow through a passageway of the valve. Armature motion is resisted by a return spring that acts on the armature, either directly or via the valve member, to bias the armature toward a position that causes the valve member to close the passageway.
In a linear solenoid valve, displacement of the armature, and also of the valve member when the valve member is displaced in exact correspondence with the armature, should theoretically bear a relationship of direct proportionality to the electric current in the solenoid coil. In other words, a graph plot of armature displacement versus electric current for such a valve should start at the origin of the graph and extend from the origin at a constant slope.
A known linear solenoid EGR valve comprises a stator having an upper stator part that is disposed at an upper end of the coil and a lower stator part at the lower end of the coil. These two parts have respective cylindrical walls, one tapered and the other non-tapered, that fit into the open center of the coil, approaching each other from opposite ends of the coil. The juxtaposed ends of the two walls are spaced apart within the open interior of the coil, and their construction and arrangement define an annular air gap disposed circumferentially around the armature. Electric current in the coil creates magnetic flux that passes from one wall across the air gap to the armature, through the armature, and back across the air gap to the other wall. The flux causes magnetic force to be applied to the armature, and the axial component of that force acts to displace the armature along the centerline of the solenoid in a substantially linear relationship of armature displacement to coil current.
Where flow through the valve is proportional to armature displacement, the functional relationship of flow to electric coil current is also substantially linear. In an EGR valve, knowledge of the relationship of armature displacement to coil current is essential to a control strategy that accurately meters exhaust gas into the engine intake system, and such linearity facilitates implementation of the control strategy in a particular engine.
For various reasons, such as smaller engines, and use of multiple EGR valves on an engine, certain automotive vehicle manufacturers are seeking to reduce the size of EGR valves, but without sacrificing desired control accuracy.
The present invention arises as a consequence of the inventor""s observations about such smaller valves. In particular, the inventor has observed that because such a valve has a smaller mass, its less massive internal mechanism is more likely to be affected by external perturbations that the valve experiences when in use. Examples of such perturbations include: pulsations in the fluid whose flow is being controlled; mechanical vibrations arising from operation of the vehicle and running of the engine that powers the vehicle; and instabilities in control strategies for a valve.
Such perturbations may be significant enough to impart disturbances to the valve mechanism in ways that are contrary to intended control strategy. Accordingly, improvements in the solenoid that would attenuate, and ideally eliminate, such effects are believed desirable, and it toward that end that the present invention is directed.
It is therefore an object of this invention to provide such improvements, particularly in linear solenoid actuators of EGR valves.
One general aspect of the invention relates to an emission control valve for controlling flow of gases with respect to combustion chamber space of an internal combustion engine. The valve comprises a valve body comprising a passageway having an inlet port for receiving gases, an outlet port for delivering gases to the combustion chamber space, a valve element that is selectively positioned to selectively restrict the passage, and a mechanism for selectively positioning the valve element. The mechanism comprises a solenoid having an electromagnet coil, a stator that is associated with the coil and that has a magnetic circuit comprising an air gap for conducting magnetic flux generated in the stator when electric current flows in the coil, and an armature that is disposed in the air gap to be displaced along an imaginary centerline by the magnetic flux. The armature is guided within a sleeve. A damping ring is disposed to act between the armature and the sleeve to damp motion of the armature within the sleeve.
The accompanying drawings, which are incorporated herein and constitute part of this specification, include one or more presently preferred embodiments of the invention, and together with a general description given above and a detailed description given below, serve to disclose principles of the invention in accordance with a best mode contemplated for carrying out the invention.